JUNCTION CITY, Calif. &

After a long day battling one of Northern California's most stubborn wildfires, dozens of weary firefighters gathered in a remote wilderness clearing near the fire's front lines to get a chopper ride back to camp.




Two veteran pilots flying a Sikorsky S-61N, a workhorse helicopter that can carry 16 passengers, had ferried out two groups and returned for another. The third group loaded up, but then there was a problem.




"They went forward a slight bit. Then the aircraft rapidly descended and hit the hillside," said Andy Mills, chief of helicopter operations for Carson Helicopters Inc., which owned and operated the chopper.




"Right now we don't know why that happened."




Federal investigators headed to the crash site Thursday to comb charred debris in an effort to determine why the aircraft went down, killing nine and injuring four. The team hoped to recover a voice-data recorder on board the helicopter, said National Transportation Safety Board spokeswoman Kitty Higgins.




"We will work to recover that recorder, but we can't guarantee its condition because of the extensive fire damage, and that may unfortunately limit its usefulness," Higgins said at a news briefing in nearby Weaverville.




According to officials with Carson, who described the crash as the company's first firefighting accident in its 50-year history, there were no obvious warnings of danger Tuesday night.




"We've talked to pilots of our other two aircraft flying in the area," Mills said. "So far it sounds to me like visibility was not an issue. It was not windy up on that ridge top." One pilot told a mechanic shortly before the fatal flight that the aircraft "was flying very well," Mills said.




Even so, the helicopter plunged out of the sky just after takeoff, officials said, coming to rest on a steep outcropping 1,000 feet below where it left the ground. The helicopter was refueled just before to the crash and burst into flames after it hit the hillside.




About 30 firefighters and other personnel in the clearing waiting for their own rides scrambled down toward the crash site in hopes of rescuing anyone who survived. According to Higgins, two survivors emerged in flames. Several witnesses reported that a third escaped without serious burns and returned to pull the fourth survivor from the wreckage.




Sheriff's officials would not begin recovering bodies from the wreckage until NTSB investigators had a chance to assess the scene. The four survivors &

three firefighters and a pilot &

were flown from the site to hospitals Tuesday night with severe injuries.




Authorities can confirm with "fair certainty" that all nine &

seven firefighters, a U.S. Forest Service employee and a pilot &

had died, said Undersheriff Eric Palmer.




The remains of the Sikorsky S-61N helicopter were smoldering for more than a day after the fiery crash, officials said.




Ten of the firefighters, including the three in the hospital, were employed by firefighting contractor Grayback Forestry, according to Kelli Matthews, a spokesman for the company.




The firefighters who died in the crash were identified by Grayback as Shawn Blazer, 30; Scott Charleson, 25; Matthew Hammer, 23; Edrik Gomez, 19; Bryan Rich, 29; and David Steele, 19. All were from southern Oregon.




Grayback said it would not release the name of a seventh victim until it could notify family members.




Carson Helicopters identified the pilot who was killed as Roark Schwanenberg, 54, of Lostine, Ore.




Schwanenberg "lived and breathed" flying to fight fires, his wife, Christine Schwanenberg, said Thursday. "He felt responsible for making a difference in this world."




The U.S. Forest Service did not immediately identify its employee, who was described as flight inspector on the helicopter.




The firefighters had been working at the northern end of a fire burning on more than 27 square miles in the national forest, part of a larger complex of blazes that is mostly contained.




Firefighters Michael Brown, 20, and Jonathan Frohreich, 18, as well as pilot Bill Coultas, 44, were being treated at the UC Davis hospital. Coultas was in critical but stable condition after — 1/2 hours of surgery for burns covering about a third of his body, while Brown and Frohreich were both upgraded to good condition Thursday afternoon and moved from the intensive care unit, according to the hospital.




Another firefighter, Richard Schroeder, 42, was upgraded from serious to fair condition at Mercy Medical Center in Redding, the hospital said.




Both pilots has over 25,000 hours of flight time between them, and the company had upgraded the 30-year-old chopper's engine, airframe and rotors three years ago, said Carson spokesman Bob Madden.




The helicopter could carry 1,000 gallons of water for firefighting, according to Carson. The chopper was not carrying any water or flame retardant when it crashed, Madden said.




With the exception of the 2001 World Trade Center attack, which killed 340 firefighters, Tuesday's helicopter crash would rank as one of the deadliest incidents in the U.S. for firefighters in the past 30 years.




Before the helicopter crash, three firefighters had been killed while on duty in California this year, including one firefighter also assigned to battle the Shasta-Trinity blazes who was killed last month by a falling tree.




On July 2, a volunteer firefighter in Mendocino County died of a heart attack on the fire line. Another firefighter was killed July 26 in when he was burned while scouting a fire.




Tuesday's accident was a painful reminder of how Grayback lost five firefighters in July 2002, when a van ferrying its workers from Oregon to a wildfire in Colorado swerved off a highway and spun out of control, Wheelock said.




"We are just right now concentrating on all the families and our employees," Wheelock said while visiting the UC Davis Medical Center in Sacramento, where two of his employees were being treated. "We are very concerned about them because we are very tight-knit."